The correct sequence of reagents for the preparation of Q and R i… — Solution | JEE Chemistry

MCQEasyJEE 2023Aromatic Compounds & Benzene

The correct sequence of reagents for the preparation of Q and R is:

A
(i) $\mathrm{CrO_3}$ , $770 \, \text{K}$ , $20 \, \text{atm}$ ; (ii) $\mathrm{CrO_2Cl_2}$ , $\mathrm{H^+}$ ; (iii) $\mathrm{NaOH}$ ; (iv) $\mathrm{H_3O^+}$
B
(i) $\mathrm{CrO_2Cl_2}$ , $\mathrm{H_3O^+}$ ; (ii) $\mathrm{CrO_3}$ , $770 \, \text{K}$ , $20 \, \text{atm}$ ; (iii) $\mathrm{NaOH}$ ; (iv) $\mathrm{H_3O^+}$
C
(i) $\mathrm{KMnO_4}$ , $\mathrm{OH^{--}}$ ; (ii) $\mathrm{MoO_3}$ , $\Delta$ ; (iii) $\mathrm{NaOH}$ ; (iv) $\mathrm{H_3O^+}$
D
(i) $\mathrm{MoO_3}$ , $\Delta$ ; (ii) $\mathrm{CrO_2Cl_2}$ , $\mathrm{H_3O^+}$ ; (iii) $\mathrm{NaOH}$ ; (iv) $\mathrm{H_3O^+}$

Answer

Correct answer:A

Standard Method

Given: A reaction sequence asks for the correct reagents for the preparation of Q and R from P.

Find: The correct option giving the reagent sequence.

From the solution, the sequence is stated as follows:

Step 1: Oxidation of benzene to benzoquinone using $\mathrm{CrO_3}$ at $770 \, \text{K}$ and $20 \, \text{atm}$ .
Step 2: Formation of phenol by further oxidation with $\mathrm{CrO_2Cl_2}$ in acidic medium.
Step 3: Neutralization with $\mathrm{NaOH}$ to form phenoxide ion.
Step 4: Acidification with $\mathrm{H_3O^+}$ to yield phenol.

Thus, the reagent order is:

\mathrm{CrO_3},\ 770\,K,\ 20\,atm \; \rightarrow \; CrO_2Cl_2/H^+ \; \rightarrow \; NaOH \; \rightarrow \; H_3O^+}

This matches Option A.

Therefore, the correct option is A.

Choosing the option with the correct reagents but in the wrong order. This is incorrect because multistep organic conversions depend on sequence. Match each reagent to the stated step before selecting the option.
Confusing acidic workup with the oxidation step. $\mathrm{H_3O^+}$ is used for acidification after base treatment, not as the primary oxidizing reagent. Keep reaction conditions separated by function.
Ignoring the final $\mathrm{NaOH}$ and $\mathrm{H_3O^+}$ sequence. This is wrong because base treatment followed by acidification is a distinct transformation step. Do not stop after identifying only the first oxidizing reagent.

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